The present invention provides a method and apparatus for improving the dynamic response or feel of a golf club as it strikes a golf ball during play. The golf swing can be divided into six major components: initial alignment coupled with alignment stability; the back swing; the forward swing; ball impact; dynamic response of the club; swing follow through. These swing components are applicable both to full swing clubs and putters.
Although there are many products and prior patents relating to adjusting the swing weight, feel, or balance of a golf club, few if any of these devices are directed towards improving the dynamic response, or feedback, of the club to the golfer at ball impact. Most prior art devices are aimed more specifically at the static or quasi-static feel of the club in the golfer's hand at the initial alignment, or during the back and forward swings. Such devices usually focus on the feel of the club itself, not the feel of the shot through the club. The importance of impact and dynamic response to the golfer's game are often overlooked.
Impact is momentary, but it is at and immediately following this critical moment that the golfer feels his shot through the dynamic response of the club. As many golfers will confess, after impact one often knows where the ball is heading without having to actually see its trajectory. The golfer has only one tactile interface to the club, and that is through his hands which grasp the club's shaft on the grip. It is thus through the golfer's hands gripping the shaft that the dynamic response of the club to the golfer's stroke is communicated. This dynamic response is a result of the vibration characteristics of the club, and the golfer often perceives it simply as feel. Thus it follows that if the club's dynamic response can be increased in this specific gripping area, the golfer will have a better feel for his shot.
The dynamic response of the club may be quantified in terms of finite element analysis and empirical modal analysis. As used herein, the term “grip end” refers to the end of the shaft to which the grip is affixed, and the term “head end” refers to the end of the shaft to which the club head is attached. Although some mathematical models of the golf club treat the grip end as a fixed boundary, the golfer's hands are coupled only viscously to the golf club. Thus the additional boundary stiffness at the grip-hand interface is negligible, and a fixed boundary condition does not apply. On the head end of the club, however, the mass of the club head relative to the shaft dominates the vibration characteristic. As a result, for finite element analysis, the club is best modeled by a beam with free-pinned boundary conditions. The pinned end corresponds to the head end while the grip end of the club represents the free end.
Mathematically, the impact of the club head against the ball is most analogous to an impulse. In response to such an input excitation, the golf club exhibits a certain modeshape, which comprises the fundamental mode and harmonics of the fundamental extending into higher frequencies. In any dynamic system, the lowest frequency mode, in this case the fundamental, has the greatest amplitude and thus exhibits the largest displacement characteristics when responding to an input excitation such as the ball-head impact. Consequently, the large-displacement, low-frequency dynamic response of the fundamental mode has the potential to provide maximum feedback to the golfer. By definition, the fundamental mode has two nodes, one near each end of the club, at which (again, by definition) the amplitude of the waveform is zero.
Finite element analysis of a pinned-free beam predicts, and empirical testing of actual golf clubs confirms, that the node of the fundamental mode near the grip end of the club (hereinafter the “grip-end node”) is located at a point that is approximately 26% of the length of the club from the grip end. This location happens to fall where most golfers grip the club. As a result, the amplitude of the fundamental mode is at a minimum at the interface of the golfer and golf club, and thus the golfer's ability to feel the dynamic response of the club is muted.
The present invention provides a method and apparatus for improving the dynamic response of the golf club by moving the grip-end node of the fundamental mode further up the shaft towards the grip end and thereby increases the amplitude of the fundamental at the golfer's interface with the club. This action in turn enhances the feel of the club to the golfer.